The invention relates to a device for clamping the trailing edge of a printing plate in a plate cylinder of a rotary printing machine, including a torsion bar disposed in a cylinder gap extending in the longitudinal direction of the plate cylinder, and braced against cheeks of the plate cylinder, clamping elements cooperating with holding elements affixed to the torsion bar, for clamping the printing plate, and an actuator provided on the torsion bar for stretching the printing plate in axial direction, the torsion bar being rotatably mounted in a support bearing at the center of the cylinder.
A conventional embodiment of this type is disclosed in the published German Patent Document DE 42 44 279 A1, wherein a printing plate, when clamped, is adjustable to changes in the printing image by stretching the substrate to be processed. With this known construction, the trailing edge of the printing plate, as viewed in axial direction, can be stretched towards both sides from a support bearing arranged at the center. In addition, in this heretofore known construction, it is possible to stretch only one or the other side, so that in the event of a single-sided application of ink to the printing substrate, a matching or adjusted stretching of the trailing edge of the plate can be performed.
In practice, the problem often occurs that the printing plate has to be compressed small amounts in the end region thereof. This option is not provided in the devices heretofore known in the prior art.
It is accordingly an object of the invention to provide a device for clamping the trailing edge of a printing plate in a plate cylinder of a rotary printing press with which, in addition to stretching the trailing edge of the printing plate, end compression is also possible.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a device for clamping the trailing edge of a printing plate in a plate cylinder of a rotary printing machine, comprising a torsion bar disposed in a cylinder gap formed in the plate cylinder and extending in axial direction thereof, clamping elements affixed to the torsion bar and cooperating with holding elements for clamping the printing plate, and actuators provided on both sides of the plate cylinder for stretching the printing plate in axial direction, the torsion bar being of bipartite construction, and the actuators, respectively, being mounted so as to be displaceable axially independently of one another.
In accordance with another feature of the invention, each of the actuators is a hollow screw.
In accordance with a further feature of the invention, the clamping device includes a cup spring arranged between each of the actuators, respectively, and the torsion bar.
In accordance with an added feature of the invention, the hollow screw is formed with a through bore for accommodating the torsion bar free of contact therein.
In accordance with an additional feature of the invention, the hollow screw is formed with an external thread cooperating with a threaded bore formed in a cheek of the plate cylinder.
In accordance with yet another feature of the invention, the clamping device includes roller bearings wherein the torsion bar is rotatably and axially adjustably mounted.
In accordance with a concomitant feature of the invention, the torsion bar has a torsionally weak construction, and the clamping elements are individually affixed to the torsion bar.
An advantage of the invention is, in particular, that the trailing edge of the printing plate can be manipulated in many ways. For example, it is possible to stretch or to compress the printing plate in specific regions.
In an advantageous embodiment of the invention, a hollow screw, respectively braced against one of the cylinder cheeks, is provided as an actuator for applying axial actuating forces in both axial directions, and a spring, preferably a cup spring, arranged between the hollow screw and the actuating shaft, eliminates play resulting from production operations from the printing-plate stretching and compressing device.
Other features, which are considered as characteristic for the invention, are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a device for clamping the trailing edge of a printing plate in a plate cylinder of a rotary printing machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: